At present, various display devices with a touch screen are being widely used and are continuously being developed. The touch screen detects that an object touches a panel, converts the touch into an electrical signal and determines whether or not there is a user's input.
The touch screen has various types such as a resistive touch screen, a pressure sensitive touch screen, a surface capacitive touch screen. The resistive touch screen senses an input by measuring a resistance value change when an object touches the screen. The pressure sensitive touch screen senses an input by measuring a surface pressure variation when an object touches the screen. The surface capacitive touch screen senses an input by measuring a surface capacitance change when an object touches the screen.
Here, in the surface capacitive touch screen, it is important to accurately sense a capacitance change caused by the input from a user. For example, when a signal which should be detected as a user's input has a specific frequency, it is possible to accurately measure the capacitance change only when signals having different frequencies from the specific frequency are appropriately filtered.